n = int(input())
s = input()
score = n
seen = set()
for i in list(s):
    if i not in seen:
        seen.add(i)
        score += 1
print(score)

# | 目的          | 正确写法                            | 错误写法            |
# | ----------- | ------------------------------- | --------------- |
# | 每个字符拆分为列表元素 | `list(s)`                       | `s.split("")` ❌ |
# | 按空格、逗号等分隔   | `s.split(" ")` 或 `s.split(",")` | –               |
